Question

这是a question I got answered yesterday的后续内容。

我正在尝试为成员函数创建一个中断线程，但我不知道这些错误是什么：

[vagrant@localhost projects]$ g++ -o test test.cpp -lpthread
test.cpp: In instantiation of ‘InterruptibleThread::InterruptibleThread(Function&&, Args&& ...)::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, Args&& ...)> [with auto:1 = void (MyClass::*)(int); Function = void (MyClass::*)(int); Args = {MyClass*, int}; std::atomic_bool = std::atomic<bool>]’:
/usr/local/include/c++/6.3.0/type_traits:2481:26:   required by substitution of ‘template<class _Fn, class ... _Args> static std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)), std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn = InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>; _Args = {std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int}]’
/usr/local/include/c++/6.3.0/type_traits:2492:55:   required from ‘struct std::__result_of_impl<false, false, InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>, std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int>’
/usr/local/include/c++/6.3.0/type_traits:2496:12:   required from ‘class std::result_of<InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>(std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int)>’
/usr/local/include/c++/6.3.0/functional:1365:61:   required from ‘struct std::_Bind_simple<InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>(std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int)>’
/usr/local/include/c++/6.3.0/thread:137:26:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>; _Args = {std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int}]’
test.cpp:41:33:   required from ‘InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]’
test.cpp:111:53:   required from here
test.cpp:36:9: error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘fxn (...)’, e.g. ‘(... ->* fxn) (...)’
      fxn( forward< Args >( args )... );

当前代码：

using namespace std;

class InterruptThreadException {};

class InterruptibleThread {
private:
    static thread_local atomic_bool* stopRef;
    static thread_local atomic_bool* pauseRef;
    atomic_bool stopFlag{false};
    atomic_bool pauseFlag{false};
    thread thrd;

public:
    friend void checkForInterrupt( );
    template < typename Function, typename... Args >
    InterruptibleThread( Function&& _fxn, Args&&... _args )
        : thrd(
                []( atomic_bool& sr, atomic_bool& pr, auto&& fxn, Args&&... args ) {
                    stopRef = &sr;
                    pauseRef = &pr;
                    fxn( forward< Args >( args )... );
                },
                ref( stopFlag ),
                ref( pauseFlag ),
                forward< Function >( _fxn ),
                forward< Args >( _args )... ) {
        thrd.detach( );
    }
    bool stopping( ) const {
        return stopFlag.load( );
    }

    void stop( ) {
        stopFlag.store( true );
    }

    void pause( ) {
        pauseFlag.store( true );
        cout << "setting pause flag: " << pauseFlag.load( ) << endl;
    }

    void start( ) {
        pauseFlag.store( false );
    }
};

void checkForInterrupt( ) {
    cout << "Pause flag: " << InterruptibleThread::pauseRef->load( ) << endl;
    cout << "Stop flag: " << InterruptibleThread::stopRef->load( ) << endl;
    while ( InterruptibleThread::pauseRef->load( ) ) {
        cout << "Paused\n";
        this_thread::sleep_for( chrono::seconds( 1 ) );
    }
    if ( !InterruptibleThread::stopRef->load( ) ) {
        return;
    }
    throw InterruptThreadException( );
}

thread_local atomic_bool* InterruptibleThread::stopRef = nullptr;
thread_local atomic_bool* InterruptibleThread::pauseRef = nullptr;

void doWork( ) {
    int i = 0;
    try {
        while ( true ) {
            cout << "Checking for interrupt: " << i++ << endl;
            checkForInterrupt( );
            this_thread::sleep_for( chrono::seconds( 1 ) );
        }
    } catch ( InterruptThreadException ) {
        cout << "Interrupted\n\n";
    }
}

class MyClass {
private:
    int myInt;
    void setInt( int i ) {
        myInt = i;
    }

public:
    MyClass( ) : myInt( 1 ) {
    }
    void myWork( int i );
    void doWork( );
};

void MyClass::myWork( int i ) {
    setInt( i );
    cout << "myInt value: " << myInt << endl;
}

void MyClass::doWork( ) {
    InterruptibleThread t( &MyClass::myWork, this, 666 );
}

int main( ) {
    MyClass mc;
    mc.doWork( );

    cout << "Press enter to exit" << endl;
    getchar( );
    return 0;
}

我尝试了编译器建议，之后得到了与fold表达式相关的错误（其中afaik是C ++ 17，我不会使用超过14的任何东西）。知道如何让这个工作吗？

我有一个不使用lambdas的工作版本，但我真的很好奇如何使用原始代码。

Answer 1

使用与指向非成员函数或其他函子的指针不同的语法来调用指向成员函数的指针。由于您的Function是void (MyClass::*)(int)，因此您需要使用语法(object.*fxn)(arg)或(objectPtr->*fxn)(arg)来调用它。

如果您可以访问C ++ 17功能，则可以使用std::invoke统一调用不同类型的callables：

InterruptibleThread( Function&& _fxn, Args&&... _args )
    : thrd(
            []( atomic_bool& sr, atomic_bool& pr, auto&& fxn, auto&&... args ) {
                stopRef = &sr;
                pauseRef = &pr;
                std::invoke(std::move(fxn), std::move(args)...);
            },
            //...

注意：我将Args&&... args更改为auto&&... args，因为Args&&...可能会导致问题。

如果您无法访问C ++ 17，则可以相当轻松地实现invoke：

template <typename Callable,
          typename... Args,
          typename = std::enable_if_t<!std::is_member_function_pointer<Callable>::value>>
decltype(auto) invoke(Callable&& c, Args&&... args) {
    return std::forward<Callable>(c)(std::forward<Args>(args)...);
}

template <typename T,
          typename T2,
          typename Ret,
          typename... FuncArgs,
          typename... Args,
          typename = std::enable_if_t<!std::is_pointer<T2>::value>>
decltype(auto) invoke(Ret (T::*c)(FuncArgs...), T2&& t, Args&&... args) {
    return (std::forward<T>(t).*c)(std::forward<Args>(args)...);
}

template <typename T,
          typename T2,
          typename Ret,
          typename... FuncArgs,
          typename... Args>
decltype(auto) invoke(Ret (T::*c)(FuncArgs...), T2* t, Args&&... args) {
    return (t->*c)(std::forward<Args>(args)...);
}

这不会执行std::invoke所做的所有事情，但会完成您需要的所有事情。

指向成员对象的指针 - 中断线程

1 个答案: